Late September might just be one of my favourite times of year. There is still warmth to be felt from the sun, the evenings begin to draw in and the air feels crisp and fresh. Blue sky, still water days feel restorative after the busy summer. And then there’s the return of the birds, a spectacle of nature that takes my breath away each year. The elegant ballerina Avocets gracing the mudflats of the upper estuary, the whistling Widgeon dabbling mud with all the decadence of open mouthed eaters and the endearing, squabbling dark-bellied brent geese (Branta Bernicla), completing a migration of 3000 miles to bring their joyful burble back to the Duck Pond.

These charming monochromatic birds spend their breeding season on the boggy arctic tundra of northern Siberia. It’s in this unforgiving environment that dark-bellied brents nest and raise their young for the first weeks of their vulnerable lives. The climate is so severe that there is a mere 2 month window of fair weather before the returning cold triggers the need to leave, and an incredible migration begins. It’s a sharp learning curve for the juveniles.

Their flight takes them south and west, following the migratory super-highway down the Baltic coast. The journey is broken by familiar rest stops; marshland, coastal grassland or suitable farmland on which to roost and feed. In places where the grazing is good they may linger a while, before pushing on for their final destination: the estuaries and wetlands of our coast. The entire journey takes no more than a matter of weeks.

The word Brent comes from the Norse brandt, meaning “burned”, and Bernicla comes from the old belief that these birds turn into barnacles in spring – historically people didn’t realise that geese migrated, they simply disappeared. Though this might seem crazy now, I still struggle with the concept that a 6000 mile round trip is the best chance of survival and breeding success these birds have.

Two races of brent geese winter in the UK. Our Dark-bellied brents that breed in Arctic Russia and migrate to the coastal and estuarine mudflats of the south coast – and pale-bellied brents from Svalbard and Franz Josef Land (archipelagos of the Barents Sea) that arrive in the North-East of England and Denmark. Other pale-bellies, from Greenland or even Canada, pass the winter in Ireland. In total, there are around 120,000 brents in the UK and over 21,000 in Ireland – together representing nearly half the world’s population. The importance of these UK wintering grounds is unequivocal.

It’s hard to imagine that the population all but died out in the 1930s. A fungal disease struck their main winter food plant, the eel-grass that grows on tidal flats and estuaries. Over the whole of its Atlantic and Pacific range, the beds of eel-grass were wiped out. Brent geese numbers dropped by three-quarters, but conservation of the wintering areas and restrictions on hunting have helped them recover.

 

On the Exe estuary in autumn, the steady arrival of family groups, flying low before gliding to a water landing at Exmouth wildlife refuge is thankfully still a familiar (and uplifting) sight. Populations have recovered and we see wintering flocks of several thousand here, but trepidation still remains. Dark-bellied Brents are classified in the UK as an Amber list species under the Birds of Conservation Concern review. The degradation of wetlands, the loss of sites to sea-level rise, and disturbance by human recreation are all factors that need to be monitored carefully. There is also the impact of climate change on their breeding grounds (where temperatures were 10 degrees warmer than usual in recent years and wildfires swept the region).

The Brents that overwinter on the Exe are incredibly site faithful. The same geese return year-on-year, guiding their juveniles on the long migration, showing them the best spots to rest at high-tide and feed as the estuary water ebbs away and eel-grass beds are exposed. For a bird that’s been recorded as living into their 30s that’s some dedication. Brents are almost always described as coming from the Arctic circle, but as they spend 6 months of the year here with us (September to March) I would argue they are ours. It makes their plight seem much more personal.

Since our project began in 2016, we’ve seen mixed breeding success for our dark-bellied brent geese. The population used to follow a classic boom-and-bust ecological relationship governed by their main breeding ground predator, Arctic foxes. In years where foxes mainly eat lemmings, brent populations boom, in a poor lemming year foxes divert their appetite to young brent geese (bust). Nowadays, however, that relationship is becoming more complex. This year, despite already seeing around a thousand brent geese feeding in the Duck Pond, I have only managed to identify one juvenile amongst them. Hopefully this will improve as we welcome the remainder of our birds throughout October and November.

Monitoring numbers of wintering waterbirds across the UK falls to an army of volunteers and dedicated birdwatchers performing organised bird surveys. Counting birds by sight is not only an incomprehensible skill (that one day I can only hope to be competent at) but also a critical part of building the evidence base for conservation science.

On the Exe, and on estuaries across the UK, the British Trust for Ornithology (BTO) wetland bird survey – WeBS for short – is performed by dedicated volunteers every month (and a huge thank you to every single one of them). Records of our wetland bird populations have been monitored in this way since the 1970s, it’s an incredibly valuable data set. This population check-in enables us to compare the ecological health of our estuary in comparison to others, and is able to warn us should a species be suffering unexplained declines.

Certainly, the importance of a winter season, where flocks are able to rest close to, and feed predominantly on, the eel-grass beds of the Exe is undisputable. Dark-bellied brents can and do move on to feed on to graze surrounding fields once supplies run out, but this food source isn’t their nutritional optimal. Winter seasons when consumption of grass and grain rather than eel-grass has been predominant, have been related to reduced breeding success in following years. Allowing undisturbed access to the Exe Wildlife Refuges is playing our part in ensuring the Exe flock comes back strong for many years to come.

Please help us ensure that these areas are left as space for wildlife, spread the word, and enjoy the incredible spectacle of overwintering birds from a distance.

To hear the burbling of Brents that I enjoy so much, why not have a listen to tweet of the day: https://www.bbc.co.uk/sounds/play/b03k5br7